A wide variety of medical endoprostheses or implants for highly diverse applications are known from the prior art. Implants according to the present invention are endovascular prostheses or other endoprostheses, such as stents (vascular stent, bile duct stent, vascular stent (including the heart and heart valve stents), mitral stent), endoprostheses for closing a patent foramen ovale (PFO), pulmonary valve stent, endoprostheses for closing an ASD (atrial septal defect), and prostheses in the region of the hard and soft tissue.
Today, stents that are used to treat stenoses (vascular constrictions) are used particularly frequently as implants. They comprise a filigree, tubular or hollow cylindrical main structure which is open at both longitudinal ends. The main structure therefore has numerous continuous openings. The main structure of the stent is often composed of individual meshes which are formed by struts having various shapes, such as zigzag or serpentine struts. Such an endoprosthesis is often inserted into the vessel to be treated using a catheter and is used to support the vessel for an extended period of time (months to years). The use of stents enables regions in the vessels to be expanded and thereby increase the lumen. Although the use of stents or other implants makes it possible to obtain an optimal vascular cross section that is necessary primarily for therapeutic success, the permanent presence of a stent—which is a foreign body after all—initiates a cascade of microbiological processes that promote e.g. inflammation of the vessel to be treated, or a necrotic change in the vessel, and/or that can result in gradual closure of the stent due to the formation of plaques or the coagulation of bodily fluid induced by a flow change or a process of infection.
To prevent restenoses, as well as inflammation and necrosis, stents or other implants are often coated with drugs that have an anticoagulant or antiinflammatory effect, for example. In that particular case it is desirable for the implants to release the pharmaceutically active substances in a targeted manner.
Stents are already known that dispense drugs from a coating which can consist of a polymer, for example. Drug depots with pumps are likewise already known. The disadvantage of the known solutions is that the pharmaceutically active substances are delivered permanently and the release cannot be controlled. In addition, the substances can only be dosed constantly, nor is it possible to determine how much of the drug is left in the reservoir or depot. The organism of the human or animal being treated is stressed unnecessarily by the permanent delivery of the contents.
Publication U.S. Pat. No. 7,060,093 B2 makes known a stent which comprises recesses (depots) in the struts. These depots contain drugs and deliver them later. The delivery of drugs from such depots is likewise difficult to control and results in an unfavorable distribution of the drug across the inner surface of the vessel being treated. This likewise results in greater stress on the organism being treated since an overdose is induced locally in order to ensure that a sufficient quantity of drug is delivered to all necessary regions of the organ being treated, which can induce toxic reactions.